EP1259670A1

EP1259670A1 - Method of manufacturing non-woven

Info

Publication number: EP1259670A1
Application number: EP01942686A
Authority: EP
Inventors: Jörgen BALOGH; Mats Averfalk
Original assignee: Fiberduk AB
Current assignee: Fiberduk AB
Priority date: 2000-01-21
Filing date: 2001-01-19
Publication date: 2002-11-27
Also published as: SE0000174L; SE515510C2; WO2001053584A1; AU2001228988A1; SE0000174D0

Abstract

The invention concerns a method of manufacturing non-woven, a non-woven fabric, a method of manufacturing a stratified composite comprising said non-woven, as well as a stratified composite. The method of manufacturing non-woven comprises the steps of forming a fibre blend containing bicomponent-type fibres, laying out the fibre blend in order to form a web, impregnating the web with latex, and drying the latex-impregnated web. A bicomponent fibre comprising a first outer component having a first melting temperature and a second core component having a second melting temperature which is higher than the first melting temperature is added as bicomponent fibres. The amount of bicomponent fibres added is at least about 50 % by weight of the fibre blend. A polymer latex which may be thermally activated at a first melting temperature that is lower than the second melting temperature is added as latex. The drying of the latex-impregnated web is carried out at a drying temperature that is higher than said first melting temperature and lower than said second melting temperature.

Description

METHOD OF MANUFACTURING NON-WOVEN

Technical Field

The present invention relates to a method of manufacturing non-woven and of manufacturing a stratified composite comprising non-woven, and to a non-woven fabric and a stratified composite manufactured in accordance with the respective methods. More specifically, the invention concerns a method of manufacturing non-woven comprising the steps of forming a fibre blend containing bicomponent-type fibres, laying out the fibre blend in order to form a web, impregnating the web with latex, and drying the latex-impregnated web. Background Art

Non-woven is a material made up mainly of individual textile fibres held together by means of bonding. Bonding is a method of textile technology for holding together fibres or threads mechanically or physicochemically (by means of sizing or melting) . Non-woven is usually classified as fabrics or flexible sheet material and is used in a wide variety of technical fields. For example, non- woven can be used as surgical drapes, outer layers of insulation, or other applications where a thin and light layer of material is desirable but where also considerable tensile strength or tear strength is required. Non- woven type materials with greater thickness can also be manufactured and thus used directly as insulation material .

A schematic representation of a conventional method of manufacturing non-woven is shown in Fig. 1. Usually the fibres are manufactured elsewhere and transported to the manufacturer of non-woven in compact bales.

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is a certain variation in the weight per unit area for each of the mats. The thickness of the web is usually about 1-3 cm.

In the next stage, the web is generally impregnated with various additives such as flame retardant, different types of size or adhesive for bonding the fibres, and colour additives. Impregnation can be done, for example, by passing the web through a fluid bath containing the desired additives. It can also be done by means of so- called foam impregnation or spray impregnation.

After the impregnation, the impregnated (wet) web is in most cases fed to a station where excess fluid is removed. This can be done by means of suction boxes, pressure and suction rollers. Following the impregnation and the removal of excess fluid, the thickness of the web is about 0.5-2 mm.

The web is then fed into an oven, where the thin sheet (the non-woven) is dried.

The non-woven dried in the oven is then stretched and wound on large rollers.

For use as, for example, body ceiling or bonnet insulation in the motor industry, the existing non-woven fabric is not satisfactory. Since non-woven is usually manufactured by special manufacturers of non-woven, and body ceilings and bonnet insulation are manufactured by other manufacturers, it is required that the various components be easily handled both individually and after they have been put together to form a partially or completely finished product. It is necessary, or at least desirable, that the non-woven should be easily handled, harmless to the environment, i.e. no ecologically harmful substances should be released during manufacture, forming of the finished product or use, and that it should be recyclable and im- part sufficient strength to the finished product.

There are numerous examples where addition of glass fibre to the non-woven is used in an attempt to meet the above demands, or requirements, concerning the handling and strength of the finished product . See for example US-A-4, 888,235, US-A-4 , 889 , 764 and US-A- , 946, 738 , all of which are derived from the same parent application, which was filed in 1987. These patent specifications disclose a vehicle body ceiling formed of a non-woven material having a thickness of about 1-3 inches (2.5- 7.5 cm) and a glass fibre content of 42 %. However, the use of glass fibre is undesirable since it may, inter alia, cause skin irritation. For setting of the fibres, the non-woven also contains up to 16 % of phenolic resin, which may release formaldehyde causing irritation to the mucosa, and which is classified by the National Chemicals Inspectorate as a carcinogen. In order to avoid the problems associated with glass fibre and the use of phenolic resin to set the fibres, several layers of non-woven may be used, as described in WO99/02335, resulting in a sandwich construction with the same strength as above without the use of glass fibre. In the sandwich construction described at least one layer consisting of two types of polyester fibres is used, one of which will melt during heat treatment bonding the remaining fibres. The different layers of the sandwich construction are bonded by thin layers of a size or the like having adhesive properties. Furthermore, it is considered necessary to coat the sandwich construction with an outer layer to give the product an acceptable appearance. The sandwich construction described thus requires a large number of additional layers, in addition to the struc- tural layers of non-woven.

Summary of the Invention

The object of the invention is to provide a solution to the above problems.

More specifically, the object is to provide a non- woven fabric that, inter alia, is harmless to the environment, that may be used as an outer layer on different insulating materials, .that may be used, alone or in com- ω ω to to ¹ μ> Π o LΠ o LΠ o LΠ

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It is preferred to add such an amount of latex that the amount of polymer added through the latex is in the range of 25-50 % by weight of the total oven-dry mass of the non-woven. Brief Description of the Drawings

The invention will be described in more detail below, with reference to the accompanying drawings, which by way of example illustrate currently preferred embodiments of the invention according to its two aspects con- cerning non-woven and stratified composite respectively. Fig. 1 is a flowchart showing the different steps of a method of manufacturing non-woven.

Fig. 2 is a drawing that illustrates how the different types of fibre and the latex material interact to bond the non-woven before the film-forming polymer has been activated.

Fig. 3 is a cross-sectional view of a bicomponent fibre of the type used in the currently preferred embodiments . Fig. 4 is an image from a scanning electron microscope (magnified 50 times) of a dried/heat treated non- woven according to a preferred embodiment . Description of a Preferred Embodiment

With reference to Fig. 2, the non-woven comprises polyester bicomponent fibres 11, consisting of an outer component that forms a sheath 11a around a core lib. The outer component 11a of the polyester bicomponent fibres has a first melting temperature T_mi of 175-180°C and the core component lib has a second melting temperature T_m2 of 260°C, i.e. higher than the first melting temperature T_ml. Furthermore, the non-woven also comprises so-called ordinary polyester staple fibres 13 having a melting and degradation temperature T_n of about 260°C. The bicomponent fibres make up about 75 % (by weight) of the fibre mass. The non-woven is impregnated with an acrylic latex, and comprises, in addition to fibres, a film-forming polymer which may be thermally activated. In order for the latex to attain a sufficiently high glass transition temperature, a modified acrylic latex is used, preferably a so-called styrene-modified acrylic latex. The polymer added through the acrylic latex has an activating tem- perature T_a that is higher than the first melting temperature T_ml but lower than the second melting temperature T_m2. The polymer constitutes about 35 % (oven-dry mass) of the non-woven.

The non-woven is particularly suited for use as one or more layers in a stratified or laminated composite.

Since the fibres 11, 13 are made of polyester, the melted phase and the fibres themselves will achieve sufficient adhesion to each other and to any adjacent layer of other materials. By forming the stratified composite at a form- ing temperature T_f that is higher than the activating temperature T_a of the polymer 12, but lower than the second melting temperature T_m2 of the bicomponent fibres 11 and the degradation temperature T_n of the staple fibres, the polymer 12 will form a film which further bonds the fibres 11, 13 of the respective layers and adjacent layers .

The manufacturing of the non-woven essentially follows a conventional method of the type described in connection with the background art. Bales of fibre of the different fibre types, polyester bicomponent fibre 11 and polyester staple fibre 13, are torn and the more or less adhering fibre lumps are inserted into a so-called first opener, where the fibre lumps are processed so that the fibres 11,13 are sepa- rated to some extent into individual fibres. Weighing of the amounts of different fibres that the non-woven is to contain is carried out in connection with the first opening.

In many applications, non-woven fabric made up of more than one type of fibre is used, the fibres commonly used being, for example, nylon fibres, viscose fibres, aramid fibres, polyester fibres or similar synthetic fibres .

After the weighing, the fibres are fed to a blender, where they are blended and further processed and opened a second time (or aired) . The blending step may be used also when only one fibre type is used; by blending fibres from different production runs (batches) from the manufacturer, the effect of possible manufacturing variations on the finished product can be reduced. After the blending, it is common to carry out some form of cleaning in order to dispose of, for example, fibre lumps and other unwanted residual products from the fibre manufacturing.

In most cases, additional steps of fibre processing (opening) are then required.

Once the fibres have been sufficiently separated, the fibre blend is fed to a carding unit . In the carding unit, the fibres are further processed and oriented so that most of the fibres are oriented in the same direc- tion. The fibre blend leaves the carding unit in the form of a thin mat, in which the fibres are oriented in the direction of transport from the carding unit, i.e. they are oriented so as to be parallel to the plane defined by the thin mat. In many cases, several mats are put to- gether, often 5-10 mats, to form a web. There are two common ways of orienting the different mats that are put together: in most cases they are either oriented the same way or alternately oriented at right angles to each other. By putting together several mats to form the web, a web with an even weight per unit area is obtained, although there is a certain variation in the weight per unit area for each of the mats. The thickness of the web is usually about 1-3 cm.

The web is then impregnated with a acrylic latex and various additives, such as flame retardant.

Impregnation is done, for example, by passing the web through a fluid bath containing the desired addi- tives. It can also be done by means of so-called foam impregnation or spray impregnation.

After the impregnation, the impregnated (wet) web is fed to a station where excess fluid is removed. This can be done by means of suction boxes, pressure and suction rollers. Following the impregnation and the removal of excess fluid, the thickness of the web is about 0.5-2 mm.

The web is then fed into an oven, where the thin flexible sheet (the non-woven) is dried. The drying is carried out at a drying temperature of 180-200°C. As long as there is fluid left in the non-woven, this will have a temperature slightly below 100°C. Once the fluid has disappeared the fibre and polymer material will be heated to a heat treatment/drying temperature T_τ of about 175-180°C. This temperature T_τ is higher than the melting temperature T_mι of the outer layer of the bicomponents, but lower than the melting temperature T_m2 of the core components. It is also lower than the activating temperature of the acrylic latex and lower than the melting temperature of the staple fibres. In the drying process the outer layer of the bicomponent fibres will melt and, due to its surface tension and the surface tension of the evaporated fluid, the heat distribution and the evaporation gradient (in the room) , will accumulate to a great extent around those places in the non-woven where the fibres abut each other. During this accumulation process the melted outer layers will attract and bind the polymer particles added through the acrylic latex. A schematic illustration of the result is shown in Fig. 2. Accumulations of material are formed, which can be compared to webbing or bat wings stretched by the fibres abutting on each other. As shown in Fig. 4 some material also sticks along the fibres in places where they do not in fact abut on each other.

The non-woven fabric dried in the oven is then stretched and wound on large rollers.

Since non-woven is usually manufactured by special manufacturers of non-woven, and body ceilings and bonnet

use and recycling. Furthermore, the stratified composite is much lighter than known sandwich constructions of the same strength, since the need for glass fibre layers and size layers has been eliminated. This is a tremendous advantage, for example in the motor industry, where even a relatively small decrease in weight changes the life cycle analysis of a car as far as the environmental impact is concerned. This is due to the fact that petrol consumption is one of the most important parameters con- cerning environmental impact and that the weight of the car greatly influences its petrol consumption.

It should be appreciated that a number of modifications of the embodiments of the invention described herein are possible within the scope of the invention, as defined in the accompanying claims.

For example, the polymer provided by the addition of latex may have an activating temperature that is lower than the first melting temperature. This might be the case when, besides temperature, a certain pressure is required in order for the polymer to be activated and to form a film.

The temperature range may, in some cases, be extended somewhat, e.g. the melting temperature of the sheath may very well be in the range of 160-200°C. Which temperature ranges that are acceptable depends on in which application the non-woven or stratified composite is to be used. For example, a body ceiling of a car must be able to withstand a new round of paintwork, at about 105°C, without beginning to soften or sag, i.e. without losing its supporting functionality. The amounts of bicomponent fibres and latex polymers may also be varied according to the application; the amount of bicomponent fibres may thus be in the range of 50-90 % of the fibre content of the non-woven. It is also conceivable that the non-woven, while remaining harmless to the environment, contains natural fibres, such as flax. Moreover, the bicomponent fibres may, in some cases, have a different configuration of core component and outer layer component. There may, for example, be several high-temperature cores in a low-temperature matrix sur- rounding and binding the different cores.

Claims

1. A method of manufacturing non-woven, comprising the steps of; forming a fibre blend containing bicomponent-type fibres, laying out the fibre blend in order to form "a web, impregnating the web with latex, and drying the latex-impregnated web, char a c t e r i s e d in that a bicomponent fibre comprising a first outer component having a first melting temperature and a second core component having a second melting temperature which is higher than the first melting temperature is added as bicomponent fibre, an amount of bicomponent fibres of at least about 50 % by weight of the fibre blend is added, a polymer latex which may be thermally activated at a first melting temperature which is lower than the second melting temperature is added as latex, the drying/heat treatment of the latex-impregnated web is carried out at a drying temperature which is higher than said first melting temperature and lower than said second melting temperature, the outer component of the bicomponent fibres melting at least partially and bonding the web, and latex is added in such an amount that the amount of polymer provided by the addition of latex is within the range of 10-60 % by weight of the total oven-dry mass of the non-woven.

2. A method according to claim 1, wherein latex is added in such an amount that the amount of polymer added through latex is within the range of 25-50 % by weight of the total oven-dry mass of the non-woven.

3. A method according to claim 1 or 2 , wherein polyester bicomponent fibres are added as said bicomponent fibres .

4. A method according to any one of claims 1-3, wherein acrylic latex is added as said latex.

5. A method of manufacturing a stratified composite, cha r a c t e r i s e d by the steps of putting together at least a first layer of non- woven, manufactured in accordance with the method of claim 1, and at least a second layer of material, compressing the layers under pressure and with supply of heat, at a temperature which is higher than said first melting temperature, higher than said activating temperature and lower than said second melting tempera- ture, causing the first component and the latex of said layer of non-woven to melt and form a film that bonds to said second layer.

6. Non-woven containing bicomponent-type fibres and a polymer, c hara c t e r i s ed in that the bicomponent fibres have a first outer component having a first melting temperature and a second core component having a second melting temperature which is higher than the first melting temperature, the bicomponent fibres exist in an amount of at least about 50 % by weight of the fibre content of the non-woven, the polymer may be thermally activated at a first activating temperature which is lower than the second melting temperature, the non-woven is heat treated at a temperature that is higher than said first melting temperature and lower than said second melting temperature, the outer sheath of the bicomponent fibres melting at least partially and bonding the non-woven and the polymer particles, and the amount of polymer provided by the addition of latex is within the range of 10-60 % by weight of the total oven-dry mass of the non-woven.

7. Non-woven according to claim 6, wherein the amount of polymer added through latex is within the range of 25-50 % by weight of the total oven-dry mass of the non-woven.

8. Non-woven according to claim 6 or 7 , wherein the bicomponent fibres are polyester bicomponent fibres .

9. Non-woven according to any one of claims 6-8, wherein said latex is an acrylic latex.

10 . A stratified composite c h a r a c t e r i s e d in that it comprises at least a first layer of non-woven of the type defined in claim 6, and at least a second layer of material, and the layers have been compressed together under pres- sure and with supply of heat, at a temperature that is higher than said first temperature, higher than said activating temperature and lower than said second melting temperature, the first component and the latex in said layer of non-woven having melted to form a film bonding to said second layer.